1. Field of the Invention
The present invention relates to a plasma display panel (hereafter PDP), and more particularly to a PDP which can keep color temperature or color deviation constant regardless the display load factor.
2. Description of the Related Art
PDP is a flat display panel which implements a 42 inch large screen. PDP has a gas discharge space where discharge gas is sealed between the front face side substrate and the rear face side substrate. By ultra-violet rays generated by the space charges, ions and electrons, which are generated by discharging in the gas discharge space, fluorescent substances formed inside are excited and the desired color display is implemented. Generally fluorescent substances for three primary colors, red (R), green (G) and blue (B) are formed in each pixel, and the color display based on the combination of the three primary colors is executed by controlling the each emission intensity in each pixel.
In this case, if the grayscale of RGB is 256, for example, a black display is executed when all the grayscales of RGB are 0, and the white display is executed when all the grayscales of RGB are 256. When the grayscales of RGB are less than 256 but are all equal, the white display with low luminance (gray) is executed.
FIG. 1 is a curve of color temperature. The abscissa is the x chromaticity coordinate, and the ordinate is the y chromaticity coordinate. The curve with 0 deviation is a black body radiation curve where the color temperature changes along the curve. Along this black body radiation curve, a bluish white is generated if the color temperature is high, and yellowish white is generated if the color temperature is low. Also, at each color temperature, a greenish white is generated if deviation shifts to the positive direction and reddish white is generated if deviation shifts to the negative direction.
For the color temperature of white created by three primary colors, it is generally said that 9000–10000K is the optimum for Japanese. And it is said that 6000K is the optimum for Europeans and Americans. White for PDP is desirable to be set to the above optimum color temperature values.
FIG. 2 are drawings depicting the relationship between the display load factor, color temperature value and color temperature deviation of a general PDP. FIG. 2A shows the relationship between the display load factor and the color temperature value of white to be displayed for three types of PDPs, and FIG. 2B shows the relationship between the display load factor and the color temperature deviation of white to be displayed for the same three types of PDPs. The display load factor is a ratio of the display load which depends on luminance and/or display area of a display image, where (1) when 256 grayscales, which is the maximum grayscale, of white is displayed on the entire display screen, and the display load factor is 100%, (2) the display load factor decreases as the ratio of white to black in the display screen decreases, and (3) the display load factor decreases as the grayscale value of white decreases even if the ratio of the white to black is the same.
As FIG. 2A shows, in the case of a PDP made by company B, for example, the color temperature value when the display load factor is 30% is 10000K, where roughly an optimum white is displayed, but as the display load factor increases, the color temperature value of white decreases and white becomes yellowish. This tendency is the same for the PDPs made by company A and company C.
As FIG. 2B shows, in the case of company A and company C, the deviation of the color temperature is almost 0 when the display load factor is about 30%, but as the display load factor increases, the deviation changes to the positive side and white becomes greenish.
It is a serious problem where white turns a color in this manner depending on the display load factor.